title: The tRNA recognition mechanism of the minimalist SPOUT methyltransferase, TrmL.
abstract: Unlike other transfer RNAs (tRNA)-modifying enzymes from the SPOUT methyltransferase superfamily, the tRNA (Um34/Cm34) methyltransferase TrmL lacks the usual extension domain for tRNA binding and consists only of a SPOUT domain. Both the catalytic and tRNA recognition mechanisms of this enzyme remain elusive. By using tRNAs purified from an Escherichia coli strain with the TrmL gene deleted, we found that TrmL can independently catalyze the methyl transfer from S-adenosyl-L-methionine to and isoacceptors without the involvement of other tRNA-binding proteins. We have solved the crystal structures of TrmL in apo form and in complex with S-adenosyl-homocysteine and identified the cofactor binding site and a possible active site. Methyltransferase activity and tRNA-binding affinity of TrmL mutants were measured to identify residues important for tRNA binding of TrmL. Our results suggest that TrmL functions as a homodimer by using the conserved C-terminal half of the SPOUT domain for catalysis, whereas residues from the less-conserved N-terminal half of the other subunit participate in tRNA recognition.
authors.affiliation: Center for RNA research, State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, The Chinese Academy of Sciences, 320 Yue Yang Road, Shanghai 200031, China.
authors.forename: Ru-Juan
authors.initials: RJ
authors.lastname: Liu
authors.forename: Mi
authors.initials: M
authors.lastname: Zhou
authors.forename: Zhi-Peng
authors.initials: ZP
authors.lastname: Fang
authors.forename: Meng
authors.initials: M
authors.lastname: Wang
authors.forename: Xiao-Long
authors.initials: XL
authors.lastname: Zhou
authors.forename: En-Duo
authors.initials: ED
authors.lastname: Wang
mesh_terms: D000595:Amino Acid Sequence; D024361:Amino Acids, Basic / Q000737:chemistry; D020134:Catalytic Domain; D003067:Coenzymes / Q000737:chemistry; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008780:Methyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D055503:Protein Multimerization; D012356:RNA, Transfer, Leu / Q000737:chemistry / Q000378:metabolism*; D012435:S-Adenosylhomocysteine / Q000737:chemistry; D012436:S-Adenosylmethionine / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D024361:Amino Acids, Basic; D003067:Coenzymes; D029968:Escherichia coli Proteins; D012356:RNA, Transfer, Leu; D012436:S-Adenosylmethionine; D012435:S-Adenosylhomocysteine; D008780:Methyltransferases; C553602:TrmL protein, E coli